1. Field of the Invention
The invention relates to a medical/surgical device and method for treating the heart, and more particularly, the invention relates to an ultrasonic device and method for creating holes in heart tissue.
2. Brief Description of the Related Art
Currently there are a number of companies using lasers to create holes in heart tissue, for example, Cardiogenesis Corporation of Sunnyvale, Calif.; PLC Systems, Inc. of Franklin, Mass.; and Eclipse Surgical Technologies, Inc. of Palo Alto, Calif.. Each of these companies are utilizing lasers as an energy source to vaporize heart tissue to create a plurality of holes in the heart for treating angina and heart ischemia.
Angina is sever cardiac pain most often due to ischemia of the myocardium. Ischemia is localized tissue anemia due to a partial or temporary obstruction of inflow of arterial blood. Ischemic tissue in the heart is usually found in the left ventricle due to a partial or temporary obstruction or constriction of the coronary arteries. The procedure of forming holes in the myocardial tissue of the heart is referred to as transmyocardial revascularization ("TMR"). The purpose of TMR is to improve blood flow to under perfused myocardium. The laser created TMR holes are generally formed in the left ventricle. The holes are typically 1 mm in diameter and are placed on a 1 cm by 1 cm grid. Depending on the extent of the angina and ischemia, the laser is used to make somewhere between 10 and 50 holes. Once the holes are created, the holes are sealed off at an exterior of the heart using pressure on the epicardial surface to prevent bleeding into the pericardium.
Studies of TMR procedures on humans have had encouraging results. For example, studies have found a two class reduction in angina in some patients following TMR surgery. This two class reduction of angina greatly increases the quality of life for patients suffering from classes III and IV angina. Patients having classes III and IV angina may not be able to carry on daily activities such as walking without sever pain and may be frequently hospitalized due to heart pain. Following TMR surgery some class III and IV angina patients experience minimal or no angina for up to two years following surgery. Although these studies show that the TMR procedure improved the patients condition and quality of life, it is not yet clear how the formation of holes in the myocardium provides this marked improvement in patient condition.
Three hypophysis for the improvement which has been observed are that 1) blood flow through the TMR channels directly perfuses the myocardium, 2) damage to heart tissue from ablation and heat of the laser causes release of growth factors that result in angiogenesis, and 3) destruction of nerve pathways mask angina and prevents pain. Because the positive results of TMR surgery last up to two years, and the channels have closed by this time, it is believed that direct tissue perfusion is not the sole reason for the observed improvement.
Currently TMR is being performed utilizing a laser source of energy which forms a hole all the way through the heart tissue. Once the holes are formed by the laser, the surgeon, must cover the hole by placing a finger on the epicardial surface until the hole clots shut or the surgeon may use a suture to close the hole. Another disadvantage of the use of a laser is the cost. The laser energy source for use in this procedure costs between about $200,000 to $700,000. This creates a high cost of performing the TMR procedure. Additionally, the laser TMR procedure vaporizes viable heart tissue.
Accordingly, it would be desirable to provide a cost effective supply of energy to create holes in heart tissue. It is also preferable that the energy delivery system does not vaporize viable heart tissue, and does not form holes all the way through the heart tissue.